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Knowledgebase Article

How does a Light Dimmer Work?


As the name suggests, light dimmers are used to dim the lights in your house. Many customers have asked me just how a light dimmer works. This article aims to explain this without making it too complicated for the lay person.

Firstly, you have to understand how the electricity comes out of the outlet in your house. In Australia we have a 240V 50 hertz A.C. system. A.C. stands for "Alternating Current" and means there is a sinusoidal wave that alternates between a positive and negative charge. It cycles between negative and positive 50 times a second, or at 50 hertz.

Now what has this got to do with a dimmer? Well, the electricity in your house goes directly into your light bulb. When all of the electricity is allowed to flow into the light bulb it will be at its brightest. What a light dimmer does is briefly stop part of the electricity flow into the bulb. This means less power goes into the bulb so it appears less bright.

The dimmer has an electronic circuit inside it that is basically like a very fast on/off switch. It switches so fast that it can turn off the flow of electricity during a small part of the wave. The more you dim the light, the bigger the section of wave that gets turned off. Because the light is being turned off around 50 times a second, your eyes can't see the flickering as the light goes on and off.

There are 3 types of dimmers - trailing edge, leading edge and universal. A leading edge dimmer turns off the light dimmer on the end (or trailing) part of the wave. A leading edge dimmer turns off the light dimmer on the leading part of the wave. These two types are to be used for different loads - a leading edge dimmer should be used with incandescent bulbs and a trailing edge dimmer should be used on lights with electronic transformers (e.g. fluorescent lights). A universal dimmer is a special type of dimmer switch that detects the type of load on the circuit and produces either a leading or trailing edge.